Stem cell self-renewal lies at the heart of metazoan development and regeneration. Stem cells self-renew and give rise to differentiated progenitor cells, a fundamental regulatory process that underlies tissue homeostasis. The paradigm is that proximity to the stem cell niche, or a microenvironment in which the stem cells reside, determines the location and size of the stem cell pool; movement away from the niche triggers differentiation. However, the molecular basis of niche regulation of stem cells is poorly understood. In this thesis, I investigate this question by examining direct niche signaling targets in the nematode Caenorhabditis elegans germline, an exceptional model of stem cells maintained in a stochastically dividing pool. In this system, a single-celled mesenchymal niche uses Notch signaling to maintain the germline stem cell (GSC) pool in a naïve state. Downstream, PUF family RNA binding proteins, FBF-1 and FBF-2 (collectively FBF), maintain stem cells at the expense of differentiation, but how Notch signaling controls FBF activity was not known. Here I describe the discovery and characterization of two direct Notch target genes, sygl-1 and lst-1, and show that they are key niche signaling effectors that molecularly link Notch signaling to downstream post-regulatory RNA network. sygl-1 and lst-1 are essential for stem cell maintenance: both are redundantly required to maintain GSCs, and either is sufficient to promote stem cell self-renewal. Both genes encode novel proteins that are spatially-restricted to the distal-most pool of cells corresponding to GSCs. Modulation of their spatial extents demonstrates that SYGL-1 and LST-1 govern the size of the stem cell pool, and this spatial restriction is critical to prevent tumorigenesis. Mechanistically, SYGL-1 and LST-1 likely control FBF activity within stem cells to repress FBF target mRNA expression. Collectively, SYGL-1 and LST-1 represent an exemplary model of niche maintenance of a stem cell pool: niche signaling activates direct effector genes to control downstream post-transcriptional RNA regulator; spatial regulation of SYGL-1/FBF or LST-1/FBF underlies progression from a stem cell state to a differentiated state.